As described in the above-identified applications, which are hereby incorporated in their entirety by reference, in the operation of a steam power plant utilizing fossil fuel as the energy source, a desulfurization gypsum is produced.
Basically the desulfurization gypsum arises from the desulfurization of the flue gas before it is released into the atmosphere. The desulfurization can be effected, for example, in a wet process by treating the flue gas in a scrubber with an aqueous scrubbing solution containing an absorption medium which contains calcium or contributes calcium ions to an absorption reaction in which a calcium salt containing sulfur in the anion is obtained.
The desulfurization gypsum which is collected in the sump of the scrubber and which can be dewatered for use as a construction material is predominantly calcium sulfate dihydrate.
For the formation of shaped bodies of desulfurization gypsum for the construction trades, a variety of processes are available. In one group of such processes, the desulfurization gypsum is initially subjected to a heat treatment to transform the calcium sulfate dihydrate to the calcium sulfate semihydrate. The shaped bodies are then formed from the calcium sulfate semihydrate. Inert components can be mixed with the calcium sulfate semihydrate in this system.
In another group of processes, the desulfurization gypsum is mixed with power-plant fly ash before or after conversion to the calcium sulfate semihydrate. Shaped bodies such as bricks or blocks, pellets or the like are formed by the application of pressure.
In the operation of fossil fuel steam power plants, so-called power-plant clarifier sludge arises as a product which must be disposed of. A portion of this power-plant clarifier sludge derives from the so-called wet de-ashing as described, for example, in LUEGER "Lexikon der Energietechnik und Kraftmaschinen", Vol. 6, 1965, pages 338, 339. As explained in this work, the wet de-ashing results in the recovery of dust and fly ash carried by the flue gas.
Another portion of the power-plant clarifier sludge derives from the decarbonization of the steam power-plant feed water and other water utilized in such power plants (ibid, page 339). The decarbonization involves a separation of carbonates and hydrocarbonates from the water to yield a reduction in the total salt content of the feed water.
The wet de-ashing and the decarbonization are so carried out that a clarifier sludge arises which consists of solid particles of an especially fine grain structure, e.g. a particle size range of 1 to 50 micrometers, in water.
In the past, this power-plant clarifier sludge as generated in the operation of a steam power plant, was dewatered, for example in a filter press, at a comparatively high cost and disposed of at special waste disposition sites. It was considered to be practically worthless.
The composition of power-plant clarifier sludge varies and will depend, to the extent that it comprises wet de-ashing products, upon the composition of the fossil fuel and to the extent that it depends upon the decarbonization products, upon the composition of the feed water.